Exemplary embodiments of the present invention relate to a driven aircraft with a fuselage and wing body and at least one drive flow passage, which runs from an air inlet directed forwards on the body surface via a jet engine through the body to a jet nozzle that opens towards the rear on the body surface.
The strategic long range bomber “Northrop B-2 Spirit” (FIG. 1) as well as the unmanned combat air vehicle (UCAV) “Boeing X-45” (FIG. 2) and “Northrop Grumman X-47 Pegasus” (FIG. 3) are cited here as examples of generic aircraft of this type. The above aircraft names and representations (FIGS. 1-3) were found during a search of the Internet in May 2010. Aircraft of this type are also described in patent publications WO 2006/039553A1, FR 2 888 211 A1, and WO 2006/049555A1.
These aircraft, cited above merely by way of example, commonly include two special features in connection with one another, namely on the one hand a more or less “minimalist” design of a fuselage and wing body (corresponding to the so-called flying-wing aircraft principle) and on the other hand a low radar signature.
A low radar signature, equivalent to a low likelihood of a discovery of the aircraft by means of radar, can be achieved or promoted, e.g., by energy-absorbing paint coats, energy-conducting seals of outer skin joints, fewer and larger instead of many small service flaps, accommodation of loads in interior ducts instead of as exterior loads and further measures.
In particular, an aircraft that is to have only an extremely low radar signature must have a very simple exterior geometry with an avoidance or targeted alignment of body surfaces and body edges. Unfavorably arranged surfaces such as, e.g., vertically aligned vertical tail plane surfaces cause so much radar backscatter that an extremely low signature can no longer be achieved. For this reason with respect to a low radar signature an overwhelming advantage results with a design of the fuselage and wing body that follows at least approximately the flying-wing aircraft principle and thus does not have a particularly marked fuselage or a flowing transition between fuselage and wings.
A basic geometry that is particularly favorable in terms of signature appears to be a simple delta configuration with a certain trailing edge sweep, which does not have a marked fuselage and as far as possible should be developable. Although a trailing edge with points can also be considered, such as e.g., with a body with wings in so-called lambda configuration (cf. e.g. FIGS. 1 and 2), a certain deterioration with respect to the radar signature results with a lambda configuration of this type. To achieve an extremely low radar signature therefore a simple delta configuration (cf. e.g. FIG. 3) is a much better solution.
The design or basic geometry of the aircraft body (in particular e.g., in the manner shown in FIG. 3) explained above and advantageously, although not indispensably, for achieving a low radar signature has at least the disadvantage of gravely impaired flight properties as far as an aerodynamically unstable flying behavior. With these body designs the so-called aerodynamic neutral point seen in the flight direction lies relatively far forward. Taking into consideration the requirement that the center of gravity of the aircraft thus likewise has to lie relatively far forward, it is difficult to properly utilize the volume (above all generously available in the rear region) of the aircraft body because front regions would have to be filled as far as possible with components of high density (such as e.g., engine(s), weapon duct(s), equipment, fuel tank(s) etc.), whereas rear areas would have to be filled with components of lower density (such as e.g., air pipes, nozzle pipes, etc.). Because there is too little space available for this in the front body region and the individual components of course cannot be distributed in the body in a completely arbitrary manner this is not so easily possible in practice.
One particular problem associated with known aircraft of the type mentioned at the outset is with respect to the drive by means of a drive flow passage starting from an air inlet via a jet engine running through the body to a jet nozzle.
With the known aircraft, one or more of these drive flow passages runs against the flight direction through the aircraft body. If the (relatively dense) engine is now arranged relatively far forward for the above-referenced reasons, accordingly the air inlet is likewise located relatively far forward, which, however, is extremely detrimental to a low radar signature. Air inlets located forward are a highly problematic component with respect to a low radar signature because the cavities formed therewith tend to radiate incident radar waves again in a very broad aspect range. A “radar glance cast” from the front on the engine is also critical because rotating engine components lead to a modulation of the reflected radar signal and in this manner can make it possible to recognize the aircraft (together with the identification of the aircraft model).
A further inherent problem of air inlets is that under sideslip angles they generate a lateral force that depends on the shape of the inlet and the mass flow rate of the adjoining drive flow passage. In particular, in yawing flight air inlets installed relatively far forward thus generate a yawing moment destabilizing the aircraft, which yawing moment has to be compensated for in some way and in particular with a missing vertical tailplane can lead to grave problems with respect to flight stability.
Exemplary embodiments of the present invention are directed to an aircraft of the type mentioned at the outset that provides a greater freedom of design with respect to the shaping of the body, in particular a body in the manner of an flying-wing aircraft with improved flight properties compared to known aircraft, and/or to achieve a reduction of the radar signature of the aircraft.
The aircraft according to the invention is configured such that at least a part of the jet engine, in particular the entire jet engine, is arranged upstream of the air inlet seen in the flight direction of the aircraft and the drive flow passage has curvature sections embodied and arranged for this in a suitable manner.
In accordance with the present invention, the conventional relative arrangement of air inlet and jet engine is abandoned and the positions of these components are “uncoupled” from one another. The aircraft according to the invention shifts the jet engine is forwards and/or shifts the air inlet to the rear compared to conventional aircraft.
Advantageously, the center of gravity of the aircraft can thus be shifted forwards, which increases flight stability (or reduces flight instability) for a fuselage and wing body with aerodynamic neutral point lying relatively far forwards. The stability problems of body designs of this type are thus considerably alleviated with the invention.
According to an embodiment the body is essentially embodied with an all-wing design. In a special embodiment the front wing edges run (preferably respectively essentially in a straight line) with positive sweep (preferably at least 40°) up to a nose of the aircraft, and the rear wing edges run (preferably respectively essentially in a straight line) with a negative sweep (preferably in the range between 10° and 30°) up to a tailpiece of the aircraft.
The positions of the jet engine and of the air inlet can be selected or adapted to the desired aerodynamic and/or radar signature-related properties of the aircraft virtually as desired. In the case of predetermined positions of jet engine and air inlet, then a flow passage connecting these components and a flow passage connecting the engine output with the jet nozzle can be established. The precise course of these flow passages can be freely selected within certain limits. In principle only the positions of the air inlet, the jet engine and the jet nozzle have to be taken into consideration as “fixed points” of these flow passages.
Since at least one part of the jet engine is arranged upstream of the air inlet seen in the flight direction of the aircraft, the drive flow passage must have at least two curvature sections for flow deflection.
At least one curvature section is necessary in order to feed the incoming air to an input (e.g., compressor stage) of the jet engine. If the jet engine is hereby provided in the “normal installation position,” that is, with thrust direction against the flight direction, two curvature sections are already necessary in the region of this feed flow passage. A further curvature section in the passage between jet engine and jet nozzle can be necessary if the jet engine is not installed exactly in the flight direction (to be more precise: antiparallel to the desired thrust direction).
However, if the jet engine is oriented forwards in the “inverted installation position,” that is, with the engine output (e.g., combustion chamber, optionally with afterburner), one curvature section is already sufficient to feed the incoming air to the engine input. However, in this case at least one second curvature section is necessary in the flow passage between the engine output and the jet nozzle.
Naturally, the curvature sections (as well as the other sections) should also be embodied and arranged as far as possible in a flow-optimized manner, that is, with low flow resistance.
In one embodiment at least one, in particular all of the curvature sections of the drive flow passage provide a flow deflection by essentially 180°. This should include in particular deflection angles in the range of 160° to 200°, for example, in the range of 170° to 190°. The curvature of the flow course caused by a curvature section can be provided in a single-axis or double-axis manner.
Further advantages of the invention are shown by the shift of the position of the air inlet to the rear are thereby rendered possible. Due to the relatively light (less dense) flow passage located between an air inlet of this type and the jet engine (arranged relatively far forwards), the advantageous forward shift of the center of gravity is promoted. Furthermore, with air inlets arranged relatively far to the rear, the problems mentioned at the outset of the generation of unstable yawing moments can be alleviated. In the event that an air inlet is provided in the center of the transverse extension of the aircraft, the same applies analogously for an otherwise possibly destabilizing pitching moment.
In one embodiment the body surface has a design that reduces the radar signature of the aircraft. In this respect, in particular designs according to an all-wing concept and/or with wings in (preferably) delta or (less preferably) lambda geometry are advantageous.
A design “that reduces the radar signature” should be present when at least for the (particularly critical) front aspect region, that is, with a “radar glance from the front” a signature is present which corresponds to a radar backscatter surface of less than 10%, in particular less than 1% of that surface that would result with a conventional design of an aircraft of the same size and basic geometry.
In this respect, the shift of air inlets to the rear rendered possible according to the invention provides the further serious advantage that air inlets of this type (at least in the front aspect region) are now difficult to recognize by radar, if they can be recognized by radar at all. Furthermore, through the curvature section present in the course of the air inflow passage a direct radar view of the jet engine is also effectively prevented when the air inlet is visible from the radar device. The (at least one) curvature section provided with the invention has an additional use in this respect to a certain extent.
In one embodiment the air inlet is arranged downstream of the center of gravity of the aircraft and/or downstream of the geometric centroid of the contour of the body seen from above seen in the flight direction. Particularly major advantages can be achieved therewith with respect to flight stability and the low radar signature.
In one embodiment the opening of the air inlet is delimited on its outside by a region of the body tapering forwards, for example tapering to a point. This represents a sometimes favorable design for a low radar signature of the air inlet. Furthermore, this design can have advantages in terms of fluid mechanics with respect to the most efficient possible air inlet. The body region widening towards the rear provides a certain “run length” for the air flowing in, before this reaches the curvature section of the drive flow passage arranged e.g., relatively closely downstream of the air inlet.
In one embodiment the drive flow passage is embodied at least in part in a two-fold manner, symmetrically to a vertical longitudinal center plane of the body. Alternatively to the “two-fold” embodiment, a three-fold, four-fold etc. embodiment is also possible.
In one embodiment, several drive flow passages including associated air inlets, jet engines and possibly also jet nozzles are arranged completely separately from one another.
In another embodiment variant at least one air inlet and/or at least one section of a flow passage and/or at least one jet engine and/or at least one jet nozzle is used as a common component for two (or more) of such drive flow passages. This can be realized in a simple manner by suitably arranged bifurcations and/or junctions in the region of flow passages. According to one embodiment of the drive flow passage (several of which can also be accommodated in the aircraft as explained above), this comprises:                A first curvature section, adjoining the air inlet, for flow deflection,        A first longitudinal section, adjoining the first curvature section and extending in the flight direction, for flow guidance in the flight direction,        A second curvature section, adjoining the first longitudinal section, for flow deflection, and        A second longitudinal section, adjoining the second curvature section and extending against the flight direction, for flow guidance against the flight direction.        
The term “section extending in the flight direction” is hereby intended to mean that the respective section bridges a certain distance seen in the flight direction. To this end it is not absolutely necessary for the respective section to run (exactly) parallel to the flight direction. Instead, a course at an angle to the flight direction or longitudinal direction of the aircraft is also conceivable, wherein, however, an angle of this type is preferably relatively small (e.g., less than 30°, in particular less than 20°). In a special embodiment the first longitudinal section and/or the second longitudinal section runs essentially in a straight line. In a special further development of this embodiment, the drive flow passage hereby has two curvature sections, which respectively provide a flow deflection by approx. 180° (e.g., in the range of 170° to 190°).
There are also different possibilities for the particular arrangement or orientation of the jet engine. In a preferred embodiment variant of the above-mentioned embodiment with first and second longitudinal sections and first and second curvature sections, it is provided, for example, that the first longitudinal section contains the jet engine. The advantage over an arrangement of the jet engine, e.g., in the second longitudinal section lies in that the flow losses incurred in the course downstream of the jet engine can be “handled” (compensated by higher engine capacity) better than flow losses or a high flow resistance upstream of the engine input.
In one embodiment at least a part of the jet engine, in particular the entire jet engine, seen in the flight direction is arranged upstream of the center of gravity of the aircraft and/or upstream of the geometric centroid of the contour of the body seen from above. This renders possible a particularly extensive improvement of the flight properties with otherwise problematic designs of the fuselage and wing body.
A preferred use of an aircraft of the type described here is the use as an unmanned reconnaissance and/or combat aircraft (UAV or UCAV) in particular with a body geometry that reduces the radar signature very extensively (e.g. by more than 99%).